Thermodynamic study of grain growth in nanocrystalline metals and its simulation by molecular dynamics

Thermodynamic stability of grain boundaries and grain growth of nanocrystalline Palladium (Pd) was examined at 800 K in this study. Aiming at this goal, Song’s, quasi-harmonic Debye approximation (QDA), and equation of state (EOS) thermodynamic models were employed to plot the Gibbs free energy curves for grain boundaries in terms of excess volume. The results of EOS and Song’s models revealed that the excess volume increased more than the critical excess volume resulting in the thermodynamic stability of nanocrystalline Pd. Consequently, based on the predictions made by the two models, the growth of nanocrystalline in metals stopped at the grain sizes less than the critical size, while the results obtained by the QDA model showed that the stoppage of the grain growth and thermodynamic stability of the nanocrystalline Pd was impossible. For this purpose, the molecular dynamics atomic simulation method was used to probe the validity of the predictions. The simulation results confirmed the grain growth of nanocrystalline Pd to be more than the critical grain size and its stoppage to be at less than that.